1. Field of the Invention
The present invention relates to a monitor such as a mass spectrometer that can detect trace molecules from a sample.
2. Background Information
Mass spectrometers are typically used to detect one or more trace molecules from a sample. For example, a mass spectrometer can be used to detect the existence of toxic or otherwise dangerous compounds in a room. Mass spectrometers are also used to analyze drug compounds in solvents. Mass spectrometers typically ionize trace molecules from a gas sample and then deflect the ionized molecules into a detector. The molecules may be contained in a liquid sample which is typically volatilized using heat and a flow of gas such as nitrogen to help break up the liquid stream into small aerosol particles. The gaseous molecules can then be ionized by techniques such as atmospheric pressure photoionization (APPI) and atmospheric pressure chemical ionization (APCI). Another method for ionizing molecules in liquid is by electrospray ionization (ESI). In the ESI method a liquid stream is charged by a voltage and the ionized molecules are released from the liquid stream in a process that creates aerosol droplets. The aerosol droplets can be further evaporated into isolated ions.
U.S. Pat. Nos. 6,211,516 and 6,329,653 issued to Syage et al. disclose a mass spectrometer that contains a photoionizer. The photoionizer includes a light source that can emit a light beam into a gas sample. The light beam has an energy that will ionize constituent molecules without creating an undesirable amount of fragmentation. The molecules can be ionized at pressures ranging from low to above atmospheric pressure. U.S. application Ser. No. 596,307 filed in the name of Syage et al. discloses embodiments of APPI sources. U.S. Pat. No. 6,534,765 issued to Robb. et al discloses an atmospheric pressure photoionization source that uses dopant molecules to increase ionization efficiency. APPI is emerging as an important technique in mass spectrometry.
It is generally desirable to provide a mass spectrometer; that can detect a number of different compounds; provides a strong parent molecular ion signal with minimal fragmentation; is minimally susceptible to interference and gives a linear response with concentration.
It would be desirable to provide a photoionizer that can handle large quantities of sample to use with various liquid flow sources such as liquid chromatography (LC) and separation columns. It would also be desirable to provide a photoionizer that ionizes analyte in liquid samples by a means other than thermal vaporization.
Finally it would be desirable to combine a photoionizer with other ionizers to extend the range of molecules that can be ionized. It is also desirable to simultaneously operate more than one ionizer and do so in a manner that provides rapid switching between different modes of operation.